In the manufacture of paper, clean bark free wood is an essential element. One of the means of separating the bark from the wood is by processing the logs through a debarking drum, which is a large rotating cylindrical steel shell normally oriented horizontal or near horizontal. The shell has a multitude of openings which provide a means for loose bark and debris to be separated from the log stream. Logs are fed into one end of the debarking drum and clean or debarked logs exit the other end. Many factors affect the efficiency of the debarking and subsequent processing operations. It has been found that uniformity of log flow is significant among these factors. If large numbers of logs are fed into a drum simultaneously, the logs are often poorly debarked, there is a tendency for large numbers of logs to subsequently exit simultaneously and create log jams in the conveyors downstream, and a generally inefficient operation results.
Currently, control of the feed rate or metering of the logs to the debarking drum is accomplished in one of two ways.
One way is by direct feed of the logs to the debarking drum feed chute with a crane utilizing small bites, or by gradually releasing the logs while they hover over the feed chute. The device that actually holds the logs on the end of the crane, a grapple, is quickly opened and closed to release small numbers of logs. It is an effective means of metering, but significantly adds to the crane utilization cycle time. Since log carrying trucks normally make deliveries only during daylight hours, a sufficient number of trucks must also be unloaded to stockpile wood for night time production. Additional lifting equipment is often dictated because of extended crane cycle time.
A second way of metering logs to the chute is by means of large live load decks and conveyors. The crane grapple quickly releases its entire load onto the live load deck and then the logs are subsequently moved into the chute by a multitude of chains driven by a large variable speed hydraulic or electro-mechanical system. This provides a live deck action which gives uniform feed and further provides surge storage so that the crane can quickly release its load. However, this method represents a significant capital investment with continuing operating and maintenance costs for the large chain transport system on the deck.